1. Field of the Invention
The present invention relates to seats, in particular an improved seat back arrangement for a seat. More specifically the present invention relates to a seat for those with a disability.
2. Related Art
It is generally desirable to make a seat as comfortable as possible, while providing adequate support and ensuring a good postural position, to a user. This is particularly so in seats for those with a disability who may spend prolonged periods in such a seat.
In addition disabled users may require a seat that provides specific support, and in addition they may place further demands, in particular in terms of robustness of the seat, on the design of a seat. Such specialist disabled seats and seating systems may be for use as a wheelchair, by attachment to a suitable wheeled base, or may be for freestanding fixed use with or without height adjustment.
Seats may incorporate an adjustable seat back which can, in particular, be pivoted about its lower attachment to the seat bottom reclined to various reclined positions to support and suit a user. In most conventional seats the seat back is fixed in the various adjusted reclined positions and the seat back provides a rigid supporting surface. Indeed a number of seats specifically seek to provide such a rigid supporting surface to support a user. However such rigid seat backs can be uncomfortable.
In addition to withstand the forces which may be applied by a user the seat must be relatively robust resulting in a relatively massive and heavy structure to withstand the loads on the seat back.
Examples of various disabled seating arrangements which incorporate seat backs which although adjustable are fixed in use are described in U.S. Pat. Nos. 5,228,747 and 5,447,356. As mentioned such seat backs can be uncomfortable due to their inflexibility.
Seats with moveable seat backs which can flex to accommodate and absorb movement and loading by a user, so called dynamic seats, are also known. These seats incorporate springs, typically gas springs, to resist movement of the seat back and absorb the loading and rearward movement of the seat back. Once loading is removed, and for example when a user leans forward, the seat back springs back into an upright position. Such seats are however less common especially in specialist seats for those with disabilities, and in general are relatively crude.
Examples of various movable seat back arrangements are described in U.S. 2005/018450; U.S. Pat. Nos. 5,501,507; 3,059,971 and 5,704,689. These however all relate to office or task chairs rather than the more specific disabled seating arrangements, and are not tailored nor adapted to meet the specific and exacting demands of disabled seats. Indeed there are problems with such arrangements that can be improved.
Overall, and in particular in the context of disabled seating, it has been found that there are problems with both the conventional adjustable seat back arrangements and the conventional dynamic seat backs, and that both arrangements can be improved.
In particular in some conventional adjustable seat back arrangements and conventional dynamic seat backs the entire seat back pad provides a single rigid support surface and/or moves as single unit. In use when a user leans back against the seat back loading is primarily via the shoulder region and upper part of the back. Resulting forces are then transferred through the lower body and seat back and the pelvis, and legs, are forced forward on the seat. This may leave the lower back unsupported and the user in an asymmetric position. With conventional dynamic backs the position of the pelvis may similarly be moved as the seat back moves.
Alternatively with some of the dynamic seat back arrangements the rearward movement of the seat back allows the pelvis to move rearward. Once the seat back then returns to the upright position, since the position of the pelvis region has been altered, the seat back may undesirably force the user forwards and/or otherwise alter the position of the user on the seat. These problems are particularly experienced by those who have particular muscular control problems, and extensor problems, for example those associated with cerebral palsy, where the user may arch their back and provide uneven loading on the seat back. As a result the seat does not provide the best support nor ensure good posture of the user within the seat.
In addition, it has also been found, especially with the relatively crude spring return movement provided by conventional dynamic seat back arrangements, that some disabled users may respond by continually moving and bouncing against the seat back. This is generally undesirable, and also means that the seat and seat back has to be reinforced to withstand such repeated impact loading.
It is therefore desirable to provide an improved seat arrangement which addresses the above identified problems and/or which more generally offers improvements or an alternative over existing arrangements